1. Field of the Invention
This invention relates generally to blow molding. In particular, this invention relates to mold assemblies for blow molding.
2. Description of Related Art
Blow molding is a cyclic process wherein a parison of material in a moldable condition is centered on the parting plane of a mold assembly, the mold assembly is closed around the parison, the parison is expanded so the exterior of the parison abuts molding surfaces defined by the closed mold assembly, the blow molded article is conditioned to be sufficiently rigid to retain its size and shape while unsupported, the mold assembly is opened and the blow molded article is removed. In general, the moldable condition of the parison is achieved when the material of the parison is at an elevated temperature, and the rigid condition of the blow molded article is achieved when the temperature of the material has been reduced. A blow molding machine comprises a press for opening and closing the mold assembly and blowing means for introducing a pressurized fluid (typically air) to expand the parison in the mold assembly. One type of blow molding equipment produces blow molded containers from preformed parisons having a closed end and a so-called “neck finish”, the parisons typically produced by injection molding away from the press and the blow molding thereof referred to as “two-stage” blow molding. Two stage blow molding machines typically include means for mechanically stretching the parison longitudinally during blow molding. Additionally, blow molding machines may comprise means for handling the molded article upon removal from the mold assembly, means for trimming waste from the molded article (single-stage machines only), and heat transfer devices to elevate the temperature of the parison to achieve the moldable condition and to reduce the temperature of the blow molded article to achieve the rigid condition.
Blow molding is commonly used for production of containers for transporting, storing and dispensing liquids wherein the blow molded article comprises a body portion and a mouth opening for filling the container and dispensing the contents therefrom. The neck finish of parisons for two-stage blow molding such containers comprises surface features such as a thread for engaging a separable closure. It is known to blow mold containers having bases formed with concave surfaces allowing the container to stand upright without other means of support. Mold assemblies for blow molding containers comprise mating mold components for forming the body portion and concave base of the container, the molding surfaces for the body portion being open to mating faces of first and second mold components and the molding surfaces for the base portion comprising a third mold component engaged by the first and second mold components. A blow molding machine press comprises movable members supporting the mold components to engage them for blow molding and to separate them for removing the molded articles. When engaged, the mating faces of the first and second mold components abut at a so-called parting plane and the third mold component seats against the first and second mold components. The third mold component closes the base opening of the first and second mold components and the base end of each container cavity defined by the first and second mold components. To remove blow molded articles, the third mold component is retracted to disengage the molding surfaces of the mold base component from the bases of the blow molded containers.
To accommodate containers having a range of volume compatible with a particular mold assembly, each of the first and second mold components advantageously comprises a replaceable height insert between the neck portion and base opening and defining the longitudinal extent of the article to be molded. The base mold component for blow molding containers with concave base portions is reciprocated between engaged and disengaged positions. Consequently, to adjust for the effective length of the first and second mold components, the third mold component likewise comprises an insert establishing the position of the molding surfaces of the base mold relative to the machine member supporting the third mold component. In known mold assemblies, disassembly of the third mold component is required to install or remove the insert, including removal of fasteners used to retain the insert in the base mold component. Hence, there is a continuing need for mold components comprising means for adjusting the position the molding surfaces without disassembly of the third mold component.